Conventionally, a throttle valve is equipped in a passage to control air drawn therethrough into an internal combustion engine of a vehicle. The throttle valve is operated according to a depression quantity of an accelerator pedal. An accelerator device is provided with such an accelerator pedal manipulated by an operator to determine an opening quantity of the throttle valve. The accelerator pedal is rotatably supported by a support member affixed to a vehicle body and is biased by a biasing component, such as a spring, toward an accelerator full-close position.
Such an accelerator device is categorized into a mechanical-type device and an electrical-type device. The mechanical-type accelerator device transmits a depression force (tread force) working on the accelerator pedal to the throttle valve via a transmission component such as a wire. The electric-type accelerator device includes a sensor for detecting the depression quantity of the accelerator pedal and transmits an electronic control unit an electric signal representing information about the depression quantity. The electronic control unit causes a throttle actuator to drive the throttle valve according to the information about the depression quantity and the like.
In a generally-known accelerator device with a tread force hysteresis characteristics, a tread force when depression of an accelerator pedal is released is less than a tread force when the accelerator pedal is depressed. In such a configuration, tread force is small when the depression of the accelerator pedal is maintained at a desired position or when the depression of the accelerator pedal is released. Therefore, burden of an operator when manipulating an accelerator pedal can be reduced.
For example, an accelerator device disclosed in JP-A-2010-158992 includes a rotor rotatable with an accelerator pedal. In the configuration of JP-A-2010-158992, a first frictional plate is equipped between the accelerator pedal and a support member. The first frictional plate is fixed to the accelerator pedal. In addition, a second frictional plate is further equipped between the rotor and the support member. As the accelerator pedal and the rotor are rotated from an idle state in an accelerator opening direction, the accelerator pedal and the rotor are spaced from each other in the axial direction. The accelerator pedal and the first frictional plate generate a frictional force therebetween, and the rotor and the second frictional plate generate a frictional force therebetween, to maintain an accelerator position corresponding to the rotation angle of the accelerator pedal.
It is noted that, according to the accelerator device disclosed in JP-A-2010-158992, it is conceivable that foreign matter sticks between the support member and the first frictional plate or between the rotor and the second frictional plate. In addition, it is further conceivable that the first frictional plate and/or the second frictional plate adhere to the support member due to, for example, an environmental variation to result in increase in frictional force of the friction member. In such a case, the accelerator pedal may not return to a full-close position where its accelerator opening is zero. When the first frictional plate adheres to the support member, the accelerator pedal is immovable. Alternatively, when the second frictional plate adheres to the support member, the rotor is immovable. In this case, the accelerator pedal is rotatable only within a clearance between a claw of the rotor and a claw of the accelerator pedal in the circumferential direction. Nevertheless, in the configuration of JP-A-2010-158992, the accelerator pedal is not enabled to return to the full-close position irrespective of the stop position of the rotor. Therefore, the accelerator pedal may not be returned to cause an idle state when depression of the accelerator pedal is released.